Mixed reality, also sometimes referred to as augmented reality, is a technology that allows virtual imagery to be mixed with a user's actual view of the real world. A see-through, head mounted, display device may be worn by a user to view the mixed imagery of virtual and real objects. Often a virtual object is registered to a real object meaning the position of the virtual object changes with the position of the real object. Real objects and their positions may be identified from image data captured by one or more cameras mounted on the display device. A one time calibration which defines a transformation from respective camera coordinates to respective display coordinates is typically performed before the see-through, mixed reality, head mounted, display is considered operational, e.g. at the factory before shipment. For rigid mixed reality display devices, a one time calibration may suffice.